This invention generally relates to a valve assembly for a pneumatic machine, and more particularly to an improved valve assembly for a pneumatic machine which includes a manually actuated means for overriding actuation of the valve.
Pneumatic machines use a gas typically air to displace at least one piston and thereby actuate the machine. Such machines include a valve assembly which controls the volume of gas that is supplied to displace each of the at least one pistons. The valves are opened by conventional mechanical or electrical means.
The mechanical or electrical means moves a spool or like member rapidly in a first direction, to open the valve and permit gas to flow to the piston. Once the valve is opened, the position of the spool or like member can only be altered by again actuating the mechanical or electrical means. Thus the flow volume of gas through the valve can not be easily adjusted or precisely adjusted. For example, the valve can be shifted in a first direction so that gas flows from the valve inlet to a first cylinder inlet. However, if it is necessary to alter the volume of gas flowing through the first cylinder inlet or redirect the gas flow to a second cylinder inlet, the electrical/mechanical means must be actuated. The valve can not be shifted to change flow to inlet to a second cylinder valve without energizing the mechanical or electrical means. Moreover, precise adjustments to the flow volume through a cylinder inlet are difficult.
Additionally, before using a pneumatic machine, it is typically necessary to test the alignment of the operative machine member that is displaced by the piston. If the operative member is misaligned, the machine will likely be damaged during operation. For example, in pneumatic printing machines, the piston is operatively connected to one or more print heads to move the printheads as the piston is displaced. Before operating such a printing machine it is necessary to check the alignment of the printheads. It is most desirable to check the alignment by slowly actuating the piston by finely adjusting and slowly increasing the gas supplied to the cylinder rather than by rapidly actuating and opening the valve. If the printhead is not in proper alignment, and the valve is opened rapidly using a conventional valve, the printheads can crash and damage the machine. By opening the valve slowly alignment can be carefully checked without incurring machine damage. Known valves for pneumatic machines make preliminary testing and checking of pneumatic machines difficult since the valve can not be adjusted without energizing the electrical/mechanical means and because making fine adjustments to the valve position is difficult.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative which permits the mechanical or electrical actuating means to be overridden to control the supply of gas to the cylinder. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.